A wind turbine of a wind power generator includes a nacelle disposed substantially horizontally on the top of a tower so as to be rotatable, a rotor head mounted on the nacelle so as to be rotatable about a substantially horizontal axis, and a plurality of (for example, three) wind turbine blades radially attached around the axis of the rotor head.
The force of the wind blowing in the axis direction of the rotor head against the wind turbine blades is converted into motive power for rotating the rotor head about the axis.
In general, in view of strength, the rotor head is composed of a cast metal (cast iron or cast steel) and is formed as a single component. In recent years, as the size of wind turbines has increased, the size and weight of the rotor heads have increased. For example, the rotor head of a wind power generator of 2 to 3 MW class weighs about 10 t. It is expected that the rotor heads of future wind power generators of 5 MW class will weigh more than 40 t.
An increase in the size of the rotor head may make it difficult or impossible to mold it as a single component from a cast metal. It also requires great effort and costs to transport the rotor head to an erection site.
Thus, there is a strong demand for a structure that can cope with an increase in the size of the rotor head.
For example, as disclosed in Patent Document 1, a rotor head that is formed as segments and is assembled at an erection site is proposed.
The rotor head is formed by joining a central core portion and three outer portions to which wind turbine blades are to be attached.
Because this enables the core portion and the outer portions having a reliable size to be formed from a cast metal, they can be produced with high quality. This also makes transportation easier because small segments are transported.
Patent Document 1:    Japanese Translation of PCT International Application, Publication No. 2004-504534